1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for driving the same, and more particularly to, a liquid crystal display device and a method for driving the same for improved luminance.
2. Discussion of the Related Art
Among display devices, cathode ray tubes (CRTs) have been primarily used for displaying images. However, recently, liquid crystal display (LCD) devices have been rapidly replacing the CRTs due to their high luminance, clear image quality, and low power driving characteristics. Generally, LCD devices use optical anisotropy of liquid crystals to produce an image by adjusting light transmissivity. Liquid crystal material is injected between two substrates of the LCD device and by applying various amplitudes of electric fields to the liquid crystal, an amount of light transmitted through the substrates can be controlled to display the image.
LCD devices are thin and light weight, provide high quality images, and can be driven with an electric power ⅓ less than CRTs having the same screen size. However, LCD devices have some limitations on the display of images as compared to the CRTs. For example, due to the properties of the liquid crystal such as viscosity and elasticity, the time for the liquid crystal to attain a desired arrangement in reaction to the electrical field is longer than 16.7 ms, which is a typical display cycle of one frame. Thus, when an image that changes every frame is displayed, motion blur may arise due to residual images being displayed. To overcome the imaging problems of the aforementioned LCD device, a variety of image processing techniques are being developed. One such technique involves adapting a driving method for a CRT to be applied to the image display of an LCD device.
FIG. 1A is an illustrative view showing an image display of a CRT. FIG. 1B is an illustrative view showing an image display of an LCD device. As shown in FIG. 1A, in the CRT, image signals are applied in an impulse form for each frame. Since images are displayed in a discontinuous manner according to the impulses, no image is displayed at intervals between the impulses. Accordingly, a phenomenon such as motion blur may not occur.
By contrast, in the LCD device, the liquid crystals continuously respond to image signals that are applied for each frame, thereby affecting the intervals between consecutive images. Accordingly, a phenomenon such as motion blur occurs. That is, as shown in FIG. 1B, a desired response (IR) and an actual response (AR) are different from each other due to the liquid crystal having a constant response speed. Therefore, in order to remove the motion blur phenomenon, the LCD may be adapted to be driven by the impulse driving technique of the CRT as illustrated in FIG. 1A.
FIG. 2A is an illustrative view showing an image signal applied to a unit pixel to imitate the impulse driving technique in an LCD device. As shown in FIG. 2A, black data BD is applied to each unit pixel during a predetermined interval of one frame. The black data BD is an image signal representing the lowest gray level to display a black image. Thus, by displaying an image of the next frame after displaying a black image during a predetermined interval of one frame, residual images from the preceding frame can be removed.
FIG. 2B is an illustrative view showing black data adapted to a continuous image signal. Such black data BD, as shown in FIG. 2B, are applied to pixels for each frame to thus remove residual image. However, if the black data BD are applied to pixels for each frame, the time during which an image is displayed by the pixels is reduced. Thus, the reduced image display time gives rise to a different problem of reduced average luminance of the LCD device.